JPH071575A - Polyester film and production thereof - Google Patents

Abstract

PURPOSE:To obtain a polyester film capable of forming surface projections hard to destruct and having relatively low hardness, capable of preventing the cutting of a partner member such as a guide while enhancing the surface abrasion resistance itself to a large extent and ideal for various industrial uses. CONSTITUTION:A polyester film is a biaxially oriented film based on polyester A and characterized by that the number of projections of at least one surface thereof is 5X10<3>/mm<2> or more and the ratio (NR) of the number of projections/ the number of particles being the ratio of the number of projections and the number of the particles contained in the surface layer on the film is 5 or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film and a method for producing the same, and more particularly to a polyester film having fine projections formed on its surface and a method for producing the same.

[0002]

2. Description of the Related Art Polyester films are widely used for various purposes. As the processing speed increases in the processing of polyester film, such as printing in packaging, magnetic layer coating in magnetic recording media, or thermal transfer layer coating in thermal transfer applications, or the required quality of the final product. With sophistication, the polyester film is required to have better surface properties such as running property and abrasion resistance. It is known that it is effective to uniformly form fine projections on the film surface in order to obtain good runnability.

A polyester film containing substantially spherical silica particles derived from colloidal silica in order to form fine projections on the surface of the film is known (for example, JP-A-59-171623). . A polyester film in which a thin layer containing particles for forming surface protrusions is laminated on a base layer is also known (for example, JP-A-2-77431).

[0004]

However, the conventional polyester film having projections formed on the surface thereof by containing particles (for example, inert particles) basically has the following two major problems. There is.

First, since particles such as inert particles different from polyester are added to polyester to form surface protrusions, voids are easily generated around the particles. When the voids are formed, the formed projections are easily broken, the film surface is easily scraped off, or the film surface is easily scratched, which causes a problem that the abrasion resistance of the film surface is deteriorated.

Further, the polyester film is often run on guide means (for example, guide rolls, guide pins) in the above-mentioned processing steps or in the use stage of the final product. In the conventional polyester film having surface projections formed by the contained particles, apart from the above-mentioned problems caused by voids, when the guide is made of metal, it may show good abrasion resistance without scratching the film surface. It is possible. However, when the guide is made of plastic, the protrusions formed by the contained particles are usually quite hard, so the problem that the surface of the plastic guide is scraped by the surface protrusions of the film and the generated powder adheres to the guide and the film It is easy to occur. This problem becomes particularly noticeable when the film is repeatedly run or at high speed.

An object of the present invention is to provide a polyester film having desired fine projections formed on the surface thereof by utilizing the crystallization of polyester essentially without depending on the contained particles, and a method for producing the same. Has uniform surface protrusions that are not easily broken, and has good wear resistance,
Another object of the present invention is to provide a polyester film in which abrasion of the guide surface is extremely small, especially when repeatedly traveling on a plastic guide.

[0008]

The polyester film of the present invention for this purpose is a biaxially oriented film containing polyester A as a main component, and the number of projections on at least one surface is 5 × 10 ³ / mm ² or more,
The number of projections / the number of particles (N _R ), which is the ratio of the number of projections to the number of particles contained in the surface layer forming the surface, is 5 or more.

That is, in the polyester film of the present invention, the ratio N _R of the number of projections formed on the surface to the number of particles contained in the surface layer is 5 or more, and the surface projections are
In essence, it is not formed by the inclusion of particles, but by utilizing the crystallization of Polyester A itself. Therefore, the problem of void generation when particles are added is substantially eliminated, and protrusions that are not easily broken are formed. N _R
Is less than 5, the proportion of projections formed by the contained particles increases, and the proportion of projections that are easily broken due to void formation increases, so that desirable wear resistance cannot be obtained.

As described above, most or all of the surface projections are formed by utilizing the crystallization of polyester A, and the number of surface projections is set to 5 × 10 ³ pieces / mm ² or more, so that the surface is finely broken. Difficult protrusions are uniformly formed on the film surface. As a result, a polyester film having a high abrasion resistance on the surface can be obtained.

Further, since the surface protrusions formed by utilizing crystallization do not have the contained particles as the core, the surface protrusions have hardness equal to or close to that of polyester A, that is, lower than the protrusions formed by the contained particles. Has hardness. Since the projections formed are relatively soft, even when the film is run on a plastic guide, the guide surface is hardly scraped, and the problems associated with the guide surface scraping are eliminated.

The formation of surface protrusions utilizing the crystallization of polyester A as described above is performed as follows. When producing a biaxially oriented film containing polyester A as a main component, at least one surface of the unstretched film is heat-treated, and then the unstretched film is biaxially stretched, whereby desired surface protrusions are formed.

By first subjecting the unstretched film to a heat treatment, the crystallization of the surface of the unstretched film, particularly the surface of the unstretched film, proceeds, and a large number of fine crystals are produced. This unstretched film is stretched biaxially, the film is oriented biaxially and the target strength of the film itself is achieved, and due to the difference in hardness between the crystal and the other part, it is caused by the fine crystals. Uniform fine surface protrusions are formed. Here, as to whether or not the surface protrusions are made of fine crystals of polyester A, etching is performed under the target protrusion in the film thickness direction with an appropriate solvent, and the cause of the formation of the protrusions is When it remains as an insoluble substance, it is a particle added from the outside or a particle deposited inside (I).
If there is substantially no insoluble matter remaining,
It can be presumed that the substance that forms the protrusion is a fine crystal (II). As the above-mentioned solvent, for example, a mixed solvent of phenol / carbon tetrachloride (weight ratio: 6/4) is preferably used. The frequency of I and the frequency of II when the field of view is set to about 1 mm ² are obtained by this method, and it is preferable that the value of II / (I + II) is 70% or more. However, the method for determining whether or not the surface protrusions are made of fine crystals of polyester A is not limited to the above method, and an appropriate method can be selected.

In the present invention, the type of polyester A is not particularly limited, but the crystallization parameter ΔTcg is 7
0 ° C or lower, preferably 65 ° C or lower, more preferably 6
It is desirable that the solution haze when dissolved in a solvent is 0 ° C. or less and 10% or less.

When the crystallization parameter ΔTcg is larger than 70 ° C., it is difficult to obtain the surface protrusions which are the target of the present invention. Even if it is obtained, the scratch resistance of the film surface is poor.

When the solution haze is more than 10%, the amount of precipitated particles or added particles in the polymer is large, a surface which does not satisfy the target of the present invention cannot be obtained, and the abrasion resistance is poor.

The polyester A is not particularly limited as long as the above conditions are satisfied, but ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylate, ethylene 2, It is particularly preferable when at least one structural unit selected from 6-naphthalate units is the main constituent.
Of these, polyesters containing ethylene terephthalate as a main constituent are particularly preferable. Two or more kinds of polyesters may be mixed, or a copolymerized polymer may be used, as long as the object of the present invention is not impaired.

In order to form a target surface protrusion, the film containing polyester A as a main component is crystallized by heat treatment before biaxial stretching as described above, but the unstretched film before biaxial stretching is used. Diameter d of spherulites present in
Is preferably in the range of 0.03 to 0.45 μm. More preferably, it is in the range of 0.10 to 0.30 μm. By controlling in such a range,
The protrusion strength and scratch resistance on the film surface after biaxial stretching are both excellent.

The polyester film of the present invention may be used as a single layer of biaxially oriented film containing polyester A as a main component or as a laminated film laminated on at least one side of a film containing polyester B as a main component. You may be asked.

The type of polyester B is not particularly limited. The polyester B preferably does not contain particles, but may contain it.

The polyester film of the present invention has a haze of 45% as a whole film, whether it is a single layer or a laminated film as described above.
It is preferably less than. If the haze is 45% or more, the surface irregularities that increase the haze are often too large, the wear resistance is poor, and the electromagnetic conversion characteristics are deteriorated in the magnetic recording medium application. The haze of the entire film is preferably less than 10%.

Next, the method for producing the polyester film of the present invention will be described more specifically. In the present invention, at least one surface of the unstretched film is heat-treated and then biaxially stretched. Here, the unstretched film refers to a state immediately after being extruded from the die and before being cooled and solidified, to a slightly stretched (up to about 2 times) slightly in the uniaxial direction. The purpose of this heat treatment is to enhance the crystallinity of the film surface before stretching to a preferable crystallinity.

In the present invention, in the process of cooling the melt-extruded film containing polyester as the main component on the surface of the cooling roll, the temperature (Tm + 1) which is higher than the glass transition temperature Tg of polyester A and higher than the melting temperature Tm by 100 ° C.
It is preferable that the unstretched film is heat-treated from the surface opposite to the surface in contact with the cooling roll at a temperature of not more than 00 ° C.), and then the unstretched film is biaxially stretched to form a desired surface protrusion. More preferably 20 ° C from Tg
High temperature (Tg + 20 ° C.) or higher and temperature higher than Tm by 80 ° C. (Tm + 80 ° C.) or lower, more preferably Tg
The temperature is 40 ° C. higher (Tg + 40 ° C.) or more and Tm or less. As a method of heat-treating the unstretched film from the surface opposite to the surface in contact with the cooling roll, hot air or radiant heat from an infrared heater can be used, but the method is not limited to this.

The surface roughness of the cooling roll is 0.2S.
Above, and 10S or less is preferable because the crystallinity of the film surface before stretching can be increased to a desired crystallinity. More preferably, the surface roughness of the surface of the cooling roll is 0.3 S or more and 8 S or less. When the surface roughness of the roll surface is less than 0.2 S, the unstretched film adheres to the cooling roll, which is not preferable. Further, if the surface roughness exceeds 10 S, desired surface protrusions may not be formed, or the film may slip on the cooling roll, which is not preferable.

In the present invention, when heat-treating an unstretched film that has been cooled and solidified, the temperature (Tcc-20 ° C.) of the surface (or surface layer) of at least one surface thereof is 20 ° C. lower than the cold crystallization temperature Tcc of polyester A. Above, the temperature (Tmc +
40 ° C.) or less so that it is kept for 0.5 to 100 seconds, and then the glass transition temperature Tg of polyester A or higher and a temperature 20 ° C. higher than Tcc (Tcc + 20 ° C.).
By biaxially stretching below, a desired surface protrusion is formed, which is preferable. More preferably, Tcc or more,
And Tmc or less, 0.5 to 50 seconds, more preferably,
The heat treatment is such that it is maintained at Tcc or more and Tmc or less for 0.5 to 20 seconds.

Further, in the present invention, the unstretched film is finely stretched in the uniaxial direction and the birefringence is 0.5 × 10 ⁻³ to 50 ×.
10 ^-3, and then the temperature of at least one surface (or surface layer) of the slightly stretched film is 20 ° C lower than the cold crystallization temperature Tcc of polyester A (Tcc-20 ° C) or more, and the cooling crystallization temperature is 40 ° C higher temperature than Tmc (T
mc + 40 ° C.) or less, heat treatment is performed for 0.3 to 50 seconds, and then the glass transition temperature T of polyester A
g or more and a temperature 20 ° C higher than Tcc (Tcc + 20
By biaxially stretching at (° C.) or less, a desired surface protrusion is formed, which is preferable. More preferably, Tcc or more and Tmc or less, 0.5 to 20 seconds, and further preferably, a temperature 10 ° C higher than Tcc (Tcc + 10 ° C) or higher and a temperature 20 ° C lower than Tmc (Tmc-20 ° C).
In the following, the heat treatment is maintained for 0.5 to 15 seconds.

As for the heat treatment method, a method of heat treatment by winding on a heating roll, a method of hot air treatment from the surface opposite to the surface in contact with the roll in the state wound on the roll, or a surface in contact with the roll in the state wound on the roll There is a method of heat treatment with an infrared heater from the opposite side, a method of heat treatment with an infrared heater between rolls, a method of heating with a stenter, and the like, but the method is not particularly limited to these.

Further, in the present invention, the temperature of at least one surface (or surface layer) of the melt-extruded film containing polyester as a main component is 70 ° C. lower than the cooling crystallization temperature Tmc of polyester A (Tmc-70 ° C.). ) Or more and at a temperature falling crystallization temperature Tmc of the polyester A or less, for 0.5 to 20 seconds, then cooled to a glass transition temperature Tg or less of the polyester A, and then biaxially stretching the unstretched film. It is preferable because a desired surface protrusion is formed.

The treatment method is, as described above, a method in which a film having a high temperature immediately after extrusion is gradually cooled to be crystallized, or a film which has been once cooled and solidified is reheated to be crystallized, or There is a method of heat treatment in the state of being slightly stretched in the uniaxial direction, and one of these methods can be carried out in the film forming process of the film to obtain a target surface morphology. Two or more of the above may be used in combination in the film forming process of the film.

Polyethylene terephthalate (PET) is preferably used as the polyester A according to the present invention. It is desirable that the polyester A contains substantially no particles. In the polymerization of polyester A, it is preferable to use antimony trioxide as a polymerization catalyst, and to use a acetate as a metal compound as a transesterification catalyst in order to reduce ΔTcg and enhance the crystal nucleating agent effect.
The acetate salt is not particularly limited, but it is particularly preferable to use a magnesium compound in order to achieve the object of the present invention. Further, it is preferable to use phosphonate as the phosphorus compound added during the polymerization of PET. However, the method for producing the polyester A is not limited to the above. To enhance the effect of nucleating agents,
Increasing the amount of catalyst added is not preferable because it causes the precipitation of internal particles and increases the solution haze.

[Physical property measuring method and effect evaluating method] The characteristic value measuring method and effect evaluating method of the present invention are as follows. (1) Number of protrusions on the film surface A flat surface of the film surface was measured by a scanning electron microscope [ESM-3200, manufactured by Elionix Co., Ltd.] using a two-detector method and a cross-section measurement device [PMS-1, manufactured by Elionix Co., Ltd. The height measurement value of the protrusions when the height is 0 is sent to an image processing apparatus [IBAS2000, manufactured by Carl Zeiss Co., Ltd.] to reconstruct the film surface protrusion image on the image processing apparatus. Next, the highest value among the individual projections obtained by binarizing the projections in this surface projection image is taken as the height of the projection, and this is calculated for each projection. This measurement was repeated 500 times at different places, and those having a height of 20 nm or more were used as protrusions to determine the number of protrusions. The magnification of the scanning electron microscope is selected to be 1000 to 8000 times. In some cases, a high-precision optical interference type three-dimensional surface analyzer (WY
KO TOPO-3D, objective lens: 40-200
It is also possible to read the number information such as the peak count obtained by double use of the high resolution camera (effective) and replace it with the value of the SEM. In order to capture the projections three-dimensionally, the film was tilted by 82.5 °, and a photograph was taken with an electron microscope (SEM) at a magnification of 10,000 to 500,000 times, and the number of projections was calculated from the average value of 100 visual field measurements. It may be converted per 1 mm ² .

(2) Number of Particles Contained in Surface Layer In the present invention, the surface layer means a portion from the film surface to a depth of 3D. Here, 3D means the average particle diameter D × 3 of the particles contained in the film. The cross section of the film is observed with a transmission electron microscope (TEM), and the number of particles existing in a portion from the surface to a depth of 3D is magnified from 3000 to 10000.
Observation is performed twice at 500 times, and the average number of particles converted per 1 mm ² is obtained.

(3) Average particle size of particles in film The polymer is removed from the film by a low temperature plasma ashing method to expose the particles. The processing conditions are such that the polymer is incinerated but the particles are not damaged as much as possible. The particles are observed with a scanning electron microscope (SEM), and the particle image is processed with an image analyzer. The magnification of the SEM is approximately 2000 to 10,000 times, and the visual field in one measurement is appropriately selected from approximately 10 to 50 μm on each side. The volume average diameter d is obtained from the particle diameter and its volume fraction with the number of particles of 5000 or more by changing the observation location. d = Σd _i · Nv _i where d _i is the particle size and Nv _i is the volume fraction thereof. When the particles are organic particles or the like and are significantly damaged by the plasma low temperature ashing method, the following method may be used. Using a transmission electron microscope (TEM), the film cross section is 30
Observe at 00-100,000 times. The section thickness of the TEM is set to about 1000Å, the location is changed and 500 or more visual fields are measured, and the volume average diameter d is obtained from the above formula.

(4) Crystallization parameter ΔTcg DSC (Differential Scanning Calorimeter) II manufactured by Perkin Elmer II
It was measured using a mold. The measurement conditions of DSC are as follows. That is, 10 mg of the sample is set in the DSC device,
After melting at a temperature of 300 ° C. for 5 minutes, it is rapidly cooled in liquid nitrogen. The temperature of this quenched sample is raised at 10 ° C./min, and the glass transition point Tg is detected. The temperature is further raised, and the crystallization exothermic peak temperature from the glass state is applied to the cold crystallization temperature Tcc,
The endothermic peak temperature based on crystal melting was taken as the melting temperature Tm, and similarly the crystallization exothermic peak temperature at the time of cooling was taken as the lowered crystallization temperature Tmc. The difference between Tcc and Tg (Tcc-Tg) is defined as the crystallization parameter ΔTcg.

(5) Solution haze of polymer 2 g of polyester was dissolved in 20 ml of a mixed solvent of phenol / carbon tetrachloride (weight ratio: 6/4) to prepare ASTM-
It was measured according to D-1003-52. The optical path length is 20
The measurement was performed as mm.

(6) Average diameter of spherulites The cross section of the film is observed by an optical or electron microscope, and the measurement is repeated until a total of 100 spherulites can be observed, and the obtained values are averaged to obtain spherulites. The average diameter was used.

(7) The film haze was measured using a haze meter according to JIS-K-6714.

(8) Birefringence The refractive index n _{MD in} the longitudinal direction and the refractive index n _{TD in the} width direction of the uniaxially oriented film are measured using an Abbe refractometer, and the difference between these two values, that is, | n _MD −n _TD Defined with |. The light source was sodium D line (wavelength: 589 nm), and the mount solution was methylene iodide at 25 ° C. and 65% RH.

(9) Film temperature A radiation thermometer, a contact surface thermometer, or a thermolabel was attached to the film for measurement. The temperature of the film in the molten state was measured by inserting a thermocouple into the radiation thermometer or the film in the molten state.

(10) Generation of powder when running on a plastic guide (plastic pin abrasion resistance) A tape running tester (manufactured by Yokohama System Laboratory Co., Ltd.) was used to slit a film into a tape having a width of 1/2 inch. TBT300D / H) is used to run on a guide pin made of polyoxymethylene (surface roughness: 1 μm at Rt) (running speed 200 m / min, running times 10 passes, winding angle: 60 degrees, running tension: 90 g). After running, observe the amount of powder generated on this pin, excellent if no powder is seen, good if the area of the adhered powder is less than 1/10 of the apparent contact area between the pin and the film, When it was 1/10 or more, it was determined to be defective. Good is desirable, but good is practically usable.

(11) Scratch resistance Continuous load type scratch strength tester HE manufactured by Shinto Kagaku Co., Ltd.
Using the scratch test with IDON-18, WY
The depth of the scratch was quantified with a non-contact roughness meter TOPO-3D manufactured by KO. [Evaluation conditions] Scratch needle: Made of sapphire Tip curvature radius 100 μm Load: 0 to 100 g / 100 mm Traveling speed: 10 m / min Depth of scratch of 0.5 μm or less: Excellent 0.5 to 1.5 μm: Good: 1.5 μm or more: Poor Excellent is desirable, but good is practically usable.

[0042]

EXAMPLES Next, the present invention will be explained based on examples. Example As polyester A, polyethylene terephthalate polymerized by a conventional method (polymerization catalyst: magnesium acetate 0.1
0% by weight, antimony trioxide 0.03% by weight, dimethyl phenylphosphonate as a phosphorus compound 0.35% by weight
Was used (intrinsic viscosity: 0.60, melting point: 25)
8 ° C, ΔTcg: 51 ° C, solution haze: 0.8%).

As the polyester B, polyethylene terephthalate polymerized by a conventional method using 0.06% by weight of magnesium acetate, 0.008% by weight of antimony trioxide and 0.02% by weight of trimethyl phosphate was used (intrinsic viscosity : 0.62, melting point: 259 ° C., ΔTc
g: 84 ° C). External particles are not particularly added to both polyesters A and B.

Examples 1 and 2 Single-layer films of polyester A were prepared. Polyester A
Pellets were dried at 180 ° C. for 3 hours, then melt-extruded at 290 ° C. by using a known extruder, wound on a casting drum having a surface temperature of 30 ° C. by an electrostatically applied casting method, and cooled, It solidified to make an unstretched film. The surface of this unstretched film that was not in contact with the drum was heat-treated using a known radiation heater under the conditions such that the film surface had the following temperature. Example 1: 150 ° C., 20 seconds heat treatment Example 2: 190 ° C., 5 seconds heat treatment After heat treatment, the film was heated at 90 ° C. in the longitudinal direction of the film.
Stretching 4 times, and then using a stenter, stretching speed 200
The film was stretched at 0% / min at 95 ° C in the width direction by 3.5 times and further heat-treated at 210 ° C for 5 seconds under a constant length to obtain a biaxially oriented film having a total thickness of 15 µm.

Examples 3, 4 A / B / A three-layered laminated film was prepared. Pellets of polyesters A and B were dried at 180 ° C. for 3 hours, fed to two extruders each, melted at 290 ° C., and combined and laminated in a rectangular confluent block (feed block) for three layers. Then, a total thickness of 15 is obtained by the same process as in Examples 1 and 2.
A biaxially oriented laminated film of μm was obtained. However, the heat treatment conditions of the unstretched film were 190 ° C. for 5 seconds.
Further, in Example 4, the stretching ratio was 4.
0 times and 4.5 times in the width direction.

Example 5 A laminated film having an A / B two-layer structure was prepared. Pellets of polyester A and polyester B were dried at 180 ° C for 3 hours, then fed to two extruders each and melted at 290 ° C to form a rectangular confluent block (feed block) for two layers.
Then, extrusion was carried out after confluent lamination, and the film was wound around a cooling roll having a surface temperature of 30 ° C. so that the surface of the polyester B layer was in contact with it by an electrostatic applied casting method.
After blowing hot air of 0 ° C., it was cooled and solidified to prepare an unstretched film. This unstretched film was stretched 3.5 times in the longitudinal direction at a temperature of 90 ° C., further stretched 4.0 times in the width direction at a stretching rate of 2000% / min at 95 ° C. using a stenter, and then a constant length. Under heat at 210 ℃ for 5 seconds,
A biaxially oriented film having a total thickness of 15 μm was obtained.

Example 6 A laminated film having an A / B two-layer structure was prepared. Pellets of polyester A and polyester B were dried at 180 ° C for 3 hours, then fed to two extruders each and melted at 290 ° C to form a rectangular confluent block (feed block) for two layers.
Then, it was extruded after being combined and laminated, and was wound around a casting drum having a surface temperature of 30 ° C. and cooled and solidified by using an electrostatic applied casting method to prepare an unstretched film. This unstretched film was stretched 1.8 times in the longitudinal direction at a temperature of 98 ° C., heat-treated for 4 seconds between rolls using an infrared heater at 230 ° C., and further, in the longitudinal direction at a temperature of 90 ° C. After stretching 0.0 times, using a stenter, stretching speed 2
It was stretched 4.5 times in the width direction at 95 ° C. at 000% / min and further heat-treated at 210 ° C. for 5 seconds under a constant length to obtain a biaxially oriented film having a total thickness of 15 μm.

Comparative Examples 1 and 2 Inactive particles were added to Polyester A (colloidal silica particles having an average particle size of 0.3 μm dispersed in ethylene glycol and added at the time of polymerization), pellets (particle content: 0. 5% by weight) was used to obtain a biaxially oriented single-layer film having a total thickness of 15 μm in the same process as in Examples 1 and 2 above. However, the heat treatment conditions for the unstretched film were 190 ° C. and 5 seconds in both Comparative Examples 1 and 2. Further, in Comparative Example 2, the stretching ratio was 4.0 times in the longitudinal direction and 5.0 times in the width direction.

Comparative Example 3 Using only polyester B, a biaxially oriented single layer film having a total thickness of 15 μm was obtained by the same process as above.

Comparative Examples 4 and 5 A biaxially oriented single-layer film was obtained using only polyester A under the following heat treatment conditions for an unstretched film. Comparative Example 4: 150 ° C., 300 seconds Comparative Example 5: 100 ° C., 600 seconds

Comparative Example 6 As polyester A, polyethylene terephthalate (polymerization catalyst: magnesium acetate 0.0
2% by weight, antimony trioxide 0.03% by weight, dimethylphenylphosphonate 0.60% by weight as a phosphorus compound
Was used) (intrinsic viscosity: 0.65, melting point: 25)
8 ° C, ΔTcg: 65 ° C, solution haze: 5.0%). Furthermore, pellets (particle content: 0.2% by weight) were prepared by adding inactive particles to this polyester A (dispersing colloidal silica particles having an average particle size of 0.45 μm in ethylene glycol and adding during polymerization). Using. Polyester B was the same as in Examples 3 to 6, and the same process as in Example 5 except that the temperature of the hot air to be blown was 73 ° C., and the total thickness was 15 μm. An axially oriented laminated film was obtained.

Comparative Example 7 Polyester A and polyester B were the same as those in Comparative Example 6, and the same method as in Examples 3 and 4 was used to obtain a laminated A / B / A three-layer structure, an unheated film and an unstretched film. . Next, this unstretched film was stretched in the longitudinal direction at a temperature of 90 ° C. for 2.7 hours.
Double stretching (measured birefringence of this uniaxially stretched film was 80 × 10 ⁻³ ), heat treated for 8 seconds between rolls using an infrared heater at 230 ° C. After being stretched 1.5 times at 90 ° C., it is stretched 4.5 times in the width direction at 95 ° C. at a stretching rate of 2000% / min using a stenter, and further at a constant length at 210 ° C. for 5 times.
Heat treatment was performed for 2 seconds to obtain a biaxially oriented film having a total thickness of 15 μm.

[0053]

[Table 1]

[0054]

According to the polyester film and the method for producing the same of the present invention, the crystallization of polyester A is utilized without depending on the contained particles to form a specific number or more of fine projections on the film surface. It is possible to suppress the generation of voids and form protrusions that are less likely to be broken, and also to prevent the guides from being scraped when traveling on a plastic guide while keeping the hardness of the protrusions relatively low. Therefore, abrasion resistance of the surface of the film itself can be significantly improved, and abrasion of a mating member such as a guide can be prevented, and a polyester film ideal for various industrial applications can be obtained.

Claims (13)

[Claims] 1. A biaxially oriented film containing polyester A as a main component, wherein the number of protrusions on at least one surface is 5 × 10 ³ / mm ² or more, and the number of protrusions and the surface are formed. A polyester film having a projection number / particle number (N _R ) which is a ratio of the number of particles contained in the surface layer to 5 or more. 2. The polyester film according to claim 1, wherein the crystallization parameter ΔTcg of the polyester A is 70 ° C. or lower. 3. The polyester film according to claim 1, which has a solution haze of 10% or less when the polyester A is dissolved in a solvent. 4. The diameter d of the spherulites existing in the unstretched film of the biaxially oriented film before biaxial stretching is 0.03 to.
The polyester film according to claim 1, which has a thickness of 0.45 μm. 5. A polyester film comprising the polyester B as a main component, and the polyester film according to claim 1 laminated on at least one surface of the film. 6. The polyester film according to claim 1, wherein the haze of the entire film is less than 45%. 7. The polyester film according to claim 1, wherein the haze of the entire film is less than 10%. 8. The method for producing a polyester film according to claim 1, wherein at least one surface of the unstretched film is heat-treated, and then the unstretched film is biaxially stretched. 9. In the process of cooling the melt-extruded film containing polyester as a main component on the surface of a chill roll, at a temperature not lower than the glass transition temperature Tg of polyester A and not higher than the melting temperature Tm by 100 ° C. (Tm + 100 ° C.),
The polyester film according to any one of claims 1 to 7, wherein the unstretched film is heat-treated from the surface opposite to the surface in contact with the cooling roll, and then the unstretched film is biaxially stretched. Production method. 10. The temperature of at least one surface (or surface layer) of the unstretched film that has been solidified by cooling is 20 ° C. lower than the cold crystallization temperature Tcc of polyester A (Tcc-
20 ° C.) and 40 ° C. higher than the temperature-lowering crystallization temperature Tmc (Tmc + 40 ° C.) or less so as to be maintained for 0.5 to 100 seconds, and then the glass transition temperature Tg or more of the polyester A and Tcc. The method for producing a polyester film according to claim 1, wherein the polyester film is biaxially stretched at a temperature (Tcc + 20 ° C.) higher by 20 ° C. or less. 11. An unstretched film is uniaxially slightly stretched to have a birefringence of 0.5 × 10 ⁻³ to 50 × 10 ^−3, and at least one surface (or surface layer) of the slightly stretched film is then stretched. The temperature is 20 ° C lower than the cold crystallization temperature Tcc of polyester A (Tcc-20 ° C) or higher and 40 ° C higher than the lowered crystallization temperature Tmc (Tmc + 40 ° C).
Below, it heat-processes so that it may be maintained for 0.3 to 50 seconds, and after that, the glass transition temperature Tg of polyester A or more
The method for producing a polyester film according to claim 1, wherein the polyester film is biaxially stretched at a temperature 20 ° C. higher than cc (Tcc + 20 ° C.) or less. 12. The temperature of at least one surface (or surface layer) of a melt-extruded film containing polyester as a main component is 70 ° C. from the temperature-lowering crystallization temperature Tmc of polyester A.
Lower temperature (Tmc-70 ° C) or higher, and polyester A
0.5 to 20 seconds below the falling crystallization temperature Tmc of
Next, the polyester film A is cooled to a glass transition temperature Tg or lower, and then the unstretched film is biaxially stretched, and the method for producing a polyester film according to any one of claims 1 to 7. 13. The method for producing a polyester film according to claim 9, wherein the surface roughness of the surface of the cooling roll according to claim 9 is 0.2 S or more and 10 S or less.